Deep-Space Experiment becomes Deep-Sea Experiment

A science experiment designed to detect deep-space neutrinos is discovering insights into everything from bioluminescent swimming bacteria to the possibility of increasing carbon pollution to underwater hurricanes.

Illustration (Credit: F. Montanet CPPM/IN2P3/CNRS-Univ.Mediterranee)

Called Antares, the completed experiment will span 10,000 square meters on the floor of the Mediterranean Sea when it's finished in 2008. Its main components include 12 electrical cables (it currently has eight) jutting 350 meters off the sea floor. On the long thin cables hang photomultiplier tubes, light detectors that are supposed to watch for light produced by fast-moving particles called muons, which are produced by neutrinos.

The photomultiplier tubes have already detected quite a bit of light, but it's probably not due to neutrinos. Rather, the detectors have been picking up large blasts of light that are too big to be from muons, as well as weak waves of light that could last for several weeks--also unlike muon light.

Biologist Christian Tamburini of the University of the Mediterranean (UM) in Marseille, France, came to investigate the results. He thinks that the long light waves are probably due to free-swimming bioluminescent bacteria. But the result is still surprising, because until now, biologists didn't know that bacteria could give off luminescence under the high-pressure conditions found at the deep-sea depths. As for the spikes of light, Tamburini predicts that they are caused by luminous fish, shrimp, or jellyfish swimming by, which all contain bioluminescent bacteria.

Launch of a Antares telescope line (Copyright Antares collaboration)

To know for sure, the scientists have decided to connect infrared cameras to the cables, which will roll film as soon as a photomultiplier detects a flash of light, and hopefully catch a glimpse of a living organism. The cameras could also take some deep-sea photos of animals that haven't been seen before, possibly revealing new exotic species.

Another "secondary" result of Antares comes from the reduction in light detected between spring 2006 and spring 2007--the light decreased by 10 times. Conceivably, this could indicate that bacteria are dying, which could be due to an input of carbon into the sea. To investigate, Tamburini plans to set up an experiment to measure the oxygen levels; since bacteria consume oxygen and emit carbon dioxide, a change in oxygen could suggest a change in the bacteria population.

Finally, the scientists are taking advantage of Antares' vast network of cables to investigate underwater currents. Interestingly, UM physicist Jürgen Brunner found that stronger currents coincide with more light spikes, as if fish were crashing into the equipment during rough storms. In spring 2006, their equipment detected a violent underwater storm, with water velocity seven times higher than expected. At the same time, the surface of the sea was relatively calm.

In the future, the scientists hope to catch remnants of a few neutrinos, which may be traveling to Earth from extreme distances in deep space, such as the edges of black holes. Studying the traces of neutrinos would enable scientists to get a glimpse into distant astrophysical objects and understand the universe on a large scale.

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